Lubricating oil resistant to cold sludge formation



nited States Patent LUBRICATING OIL RESISTANT TO COLD SLUDGE FORMATION Harvey E. Alford, Amherst, Ohio, assignor to The Standard Oil Company, Cleveland,0hio, a corporation ofOhio No Drawing. Filed Dec. 31, 1956, Ser. No. 631,512

6 Claims. (Cl. 252-18) .This invention relates to lubricating oil additives useful in the preparation of lubricating oil compositions having a lessened or substantially no tendency to form cold sludge and, more particularlyfto lubricating oil compositions comprising an alkaline detergent, an antioxidant and an organic disulfide.

When an engine is operated during cold weather and in light duty stop-and-go" operations, it rarely is heated to operating temperature for any substantial portion of the driving time. When the temperatures in the crankcase are below operating temperatures, contaminants enter the crankcase by way of blow-by. These contaminants are not dissipated because of the low operating temperatures of the oil, and have an opportunity to react or to catalyze reactions in the oil. These reactions result in the formation of what is'called cold sludge, a black, mayonnaise-like substance. One of the most important problems today is how'to combat cold sludge, because most cars used in city driving are subjected to this type of driving conditions during cold weather.

'It has now been determined that when oil containing an alkaline sulfonate type detergent, and a thiophosphate type antioxidant as additives has added thereto an organic disulfide, the oil does not develop cold sludge when the engine is operated at low temperatures for long periods of time. It is thought that this combination of additives is effective because it destroys the contaminants which enter the oil. These contaminants are thought to include organic peroxides and hydroperoxides. The peroxides are capable of catalyzing reactions that leadto the formation of high polymers, and it is'believed that high polyme rs are major components of cold sludge. Accordingly,

- the effectiveness of the additive of the invention is thought to depend'upon its abilityt'o react with peroxides to destroy them, and the additive has been evaluated on the basis of a screening test determining decomposition of cumene hydroperoxide at 100? F.

The alkaline sulfonate type detergent and the thiophosphate type antioxidants are well known in' the lubricating oil additive art. The preferred alkalinesulfonate type detergent is formed from barium octadecylsulfohate and barium carbonate. This additive is well know-n and needs no further description. The barium carbonate is thought to neutralize the acids that are formed. The preferred antioxidant is zinc octyl dithiophosphate which has a molecular weight of about 321.4 and has the formula ZnC H PS(S). ltis the zinc salt of aphosphorus pentasu-lfide-octyl mercaptan reaction product. The zinc octyldithiophosphate is an antioxidant and, in addition, inhibits corrosion and wear. i A

The organic disulfide has the general formula RSSR, where R is a hydrocarbon radical having from 3 tol8 carbon atoms, preferably from 3 to 8 carbon atoms, and can be aliphatiqaryl, alka ryl, and aralkyl; for example, propyl butyl, hexyl, octyl, decyl, dodecyl,tetradecyl, hexadecyl and octadecyl; phenyl'fbenzyl, methylbenzyl, methylphenyl, xyly-l, naphthyl, octylphenyl, nonylyphenyl, dodecylyphenyl, trimethylbenzyl, methyethylbenzyl and 2,964,474 teat? .34 9 0 ice propylbenzyl. These are known compounds, readily prepared by conventional procedures using sodium disulfide and the corresponding chlorinated hydrocarbon; the chlorine-beingafiixedto the carbon atom which is to be attached to'the disulfide chain.

Very small'amounts of the additives of the invention will give a marked improvement in lessening theform'ation of cold sludge. 'As little as 1.0% of the totalj'mixture of additives is effective, and amounts between 2% and 10% are preferred. 'Use'of amounts in excess of 20% usually cannot be justified economically. Of the total mixture of additives, the disulfide is present in an amount within the range from 8 to'70 parts by weight (p.b.w.). The other three ingredients are combined and are present in an amount of 35 to 135 p.b.w. 'In this combination, the barium octadecyl sulfonate is present in an amount within the range from 20 to 60 p.b.w., the barium carbonate in an amount within the range from 10 to 30 p.b.w., and the zinc octyl dithiophosphate in an amount within the range from 15 to 45 p.b.w.

The additives of the invention can be used to improve the cold sludge characteristics of any petroleum hydrocarbon oil of lubricating viscosity. The S.A.E. viscosities for lubricating oils range from No. 10 to No. 70. Oils having S.A.El Nos. 10 to 40 have a viscosity within the range from to 255 SSU at' F., and those oilshaving S.A.E. Nos. 40 to 70 have a viscosity within the range from 80 to 150 SSU at 210 F. The acidtreated and solvent-extracted oils are equally useful in'the compositions of the invention; The oils canbeblended from finished neutral oils of light and heavy viscosities and can include suitable bright stocks. It can also include other conventional additives such as V.I. improvers. It is impossible here to give a complete description of the various methods used in the preparation of lubricating oils, but reference is made to the text by Georgi, entitled Motor Oils and Engine Lubrication, published by Reinhold Publishing Corporation, New York (1950), a chapter V, wherein the various types of lubricating oils are discussed fully. Any of the oils mentioned therein can be employed in the composition of the invention.

. The compositionof the invention is prepared simply by mixing'the additives, either singly or together,"with the oil, at-'roomtemperature. The"additives are soluble or dispersible'in the oil, anddisp'er's'e therein instantaneously. No solvents are required but the-additivescan be" placed in solution in a hydrocarbon.

The following examples represent, in the opinion of the inventor, the best embodiment of his invention.

In theexamples, the effectiveness of the additive to decompose peroxides was determined by a screening test involving decomposition of cumene hydroperoxide at100 F. Fifty (50) grams of a cetane or solvent-extracted neutral oil SSU at 210 F.) was used as the solvent. One solution was made by adding 2.25% of a mixture comprising 40 p.b.w. barium octadecylsulfon-ate, 20 p.b.w. barium carbonate, and 28 p.b.w. Zincoctyldithiophosphate. Another solution was made by adding the disulfide in a concentration of 0.1 equivalent per equivalent of peroxide. A third solution contained both. All were heated at 280 F. for four hours while air was passed through at a rate of 35 liters per hour." To each solution w asathen added 5% of cumene hydroperoxide, and the solutions were heated for two hours at 100 F. The amount of peroxide To this was added 40 cc. of isopropanol and 2 cc. of

glacial acetic acid. The mixture was heated to reflux, and 10 cc. of saturated sodium iodide solution was added. Thereafter, the mixture was refluxed for five minutes,

cc. of distilled water was added, and the mixture titrated was 0.1 n sodium thiosulfate.

EXAMPLES 1 AND 2 A solution was prepared containing 2.25% by weight of a mixture of 40 p.h.w. barium octadecylsulfonate, molecular weight 783.4, formula Ba(S1O C l-l 20 p.b.w. barium carbonate, and 28 p.b.w. zinc octyldithiophosphate ZnC H PS( molecular weight 321.4, in solvent-extracted neutral oil, 140 SSU at 210 F. Separate additional solutions were prepared of 0.58% di-N- butyl-disulfide (0.1 equivalent) and 0.8% dibenzyldisulfide (0.1 equivalent) using this solvent-extracted neutral oil alone, and the same oil containing the sulfide and the barium octadecylsulfonate, barium carbonate and zinc octyldithiophosphate. All of these solutions then were tested by the screening test described above, after heat treatment for four hours at 280 F. with air-blowing at 35 liters per hour. The results were as follows:

Table I Relative Example Amounts No. Compound Percent of Peroxide Decomposed Control Mixture of 40 p.b.w. Barium 2.25 100 Octadecylsult'onate, 2O p.b.w. Barium Carbonate, and 28 p.b.w. Zinc Octyldithtophosphate. Dim-butyi-disulfide only". 0.58 12.7 Contro1+di-n-butyl-disulfid 2.25+0.58 143. Dibenzyl disulfidc only 0.8 11.0 Control+dibenzy1 disulfide.... 2.25+0.8 140.

A comparison of the results for Examples 1 and 2 with the control shows that the two groups of additives together are far superior to either alone. The combination of additives in accordance with the invention gives a synergistic effect on the decomposition of cumene hydroperoxide.

EXAMPLE 3 The above tests were repeated, this time employing compositions in which the additives were dissolved in cetane rather than in the solvent-extracted neutral oil, and the additives were not subjected to a prior heat treatment before testing. The results obtained were as fol- Once again, the mixture of additives of the invention is far superior.

In order to determine the effect of the additives of the invention on the formation of cold sludge in an automobile engine, engine tests were conducted on oils of the composition hereinafter indicated. The tests were conducted in a single-cylinder ethyl engine under the following conditions:

Table III Tem- Jacket Time (Hrs) R.P.M perature, Tempera- AFR F. ture, F.

2 1,280 :1:5 100i5 l Approx. 921 1, 280 300:1:5 210-l-2, 5 13:1

Test Duration: 15 cycles, 60 hours. Oil Charge: 2,000 cc.

The effect of the additives in the engine was determined by the amount of pent-ane insolubles that were formed in the oil. The result of the tests are shown in the following table:

I 4 hours at 280 F. with air-blowing at 35 liters per hour.

It is evident that the combination of additives in accordance with the invention is far superior to either alone, in that much less pentane insolubles are formed in the oil. Heat treatment of the additive mixture prior to use is not significant I claim:

1. An additive for a mineral lubricating oil for the lessening of cold sludge formation in operation of a lubricating oil at low temperatures, consisting essentially of 20 to 60 parts by weight barium octadecyl sulfonate, from 10 to 30 parts by weight barium carbonate, from 15 to 45 parts by weight zinc octyl dithi-ophosphate, and from 8 to 70 parts by weight of an organic disulfide having the formula RSSR, where R is a hydrocarbon group having from 3 to 18 carbon atoms.

2. An additive in accordance with claim 1, in which the organic disulfidc is di-n-butyi-disulfide.

3. An additive in accordance with claim 1, in which the organic disulfide is dibenzyl disulfide.

4. A mineral lubricating oil composition consisting essentially of a mineral lubricating oil and an amount of an additive in accordance with claim 1 within the range from 1% to 20% sufficient to lessen cold sludge formation during operation of the oil at low temperatures.

5. A mineral lubricating oil composition in accordance with claim 4, in which the organic disulfide. is di-n-butyldisulfide.

6. A mineral lubricating oil composition in accordance with claim 4, in which the organic disulfide is dibenzyl disulfide.

References Cited in the file of this patent UNITED STATES PATENTS 2,110,281 Adams et al. Mar. 8, 1938 2,257,890 Sloane Oct. 7, 1941 2,369,632 Cook et a1 Feb. 13, 1945 2,398,415 Denison et al Apr. 16, 1946 2,398,416 Denison Apr. 16, 1946 2,451,345 McNab Oct. 12, 1948 2,501,731 Mertes Mar. 28, 1950 2,676,925 Lindstrom et a1. Apr. 27, 1954 

1. AN ADDITIVE FOR A MINERAL LUBRICATING OIL FOR THE LESSENING OF COLD SLUDGE FORMATION IN OPERATION OF A LUBRICATING OIL AT LOW TEMPERATURE,CONSISTING ESSENTIALLY OF 20 TO 60 PARTS BY WEIGHT BARIUM OCTADECYL SULFONATE, FROM 10 TO 30 PARTS BY WEIGHT BARIUM CARBONATE, FROM 15 TO 45 PARTS BY WEIGHT ZINC OCTYL DITHIOPHOSPHATE, AND FROM 8 TO 70 PARTS BY WEIGHT OF AN ORGANIC DISULFIDE HAVING THE FORMULA RSSR, WHERE R IS A HYDROCARBON GROUP HAVING FROM 3 TO 18 CARBON ATOMS. 